OBJECTIVE To understand the dynamics of accommodation and presbyopia RESULTS These studies are generating new information about the pathophysiology of presbyopia in the rhesus monkey, the only known animal model for the human condition. DISCUSSION We implanted an electrode into the Edinger-Westphal nucleus of iridectomized rhesus monkeys between the ages of 8 and 22 yr. We determined baseline real-time dynamics of ciliary muscle, lenticular and zonular movement in response to midbrain stimulation by digital image analysis of Scheimpflug slit lamp and goniovideographic recordings. We performed various surgical ablations including extra- and intra-capsular lens extratcion, posterior capsulotomy and complete posterior capsulectomy following extracapsular lens extraction and regional zonulolysis, and have recorded some preliminary alterations in baseline real-time accommodation dynamics. FUTURE DIRECTIONS Further analysis will be done on images recorded from the surgically manipulated eyes to determine the role of the ablated structures in the accommodative process. KEY WORDS ciliary muscle, lens, zonule, capsulotomy , zonulolysis, midbrain, aniridia, electrode FUNDING NEI EY10213 PUBLICATIONS Croft MA, Glasser A, Kaufman PL The relationship between ciliary muscle function and the lens. Invest Ophthalmol Vis Sci 39(4):S312, 1998 (ARVO Abstract). [A] Glasser A, Kaufman PL Dynamics of refractive changes and lens and ciliary body movements in rhesus monkey eyes during Edinger-Westphal nucleus stimulated accommodation Vision Science and Its Applications, Technical Digest Series 1998, Vol 1, Washington, DC, Optical Society of America, pp 172-175. [J] Croft MA, Kaufman PL, Crawford KS, Neider MW, Glasser A, Bito LZ Accommodation dynamics in aging rhesus monkeys. Am J Physiol. 275 (Regulatory Integrative Comp Physiol 44) R1885-R1897, 1998. [J]